Diversity signaling system



Dec. 1, 194.2. E.$. PURINGTON 2,303,493

DIVERSITY SIGNALING SYSTEM Filed May 17, 1940 4 Sheets-Shet 1 AMPLIFIER INVENTOR ELLISON s iymsTou.

BY y

ATTORNEY Dec. 1, 1942. I I pURlNGTON 2,303,493

DIVERSITY SIGNALING SYSTEM Filed May 1'7, 1940 4 Sheets-Sheet 2 m E o- E u -o m INVENTOR nusowggmcrou.

M-u-OL/ m m o 0 ATTORNEY Dec. 1, 1942.

Filed May 17, 1940 ELLS BY I

4 Sheets-Sheet 5 INVENTOR l N GT 0 N.

ATTORNEY- I Dec. 1, 1942. E PUR|NGTONI 2,303,4Q3

DIVERSITY SIGNALING SYSTEM Filed May 17, 1940 4 Sheets-Sheet 4 i q INVENTOR ELLISON s. P RINGTONJ ATTORNEY l aieriied Dec. 1, 1942 DIVERSITY SIGNALING SYSTEM Ellison S. Purington, Gloucester, Mass, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application May 1'7, 1940, Serial No. 335,672

8 Claims.

"This invention relates to selective systems of communication, and especially to a system in which a message is conveyed by a plurality of channels.

The invention provides for the normal reception on each of the channels, and provides further for automatic means for cutting out of operation :any channel that is being interfered with.

It further provides that in case any channel is interfered with and thereby withdrawn from operation, then the sensitivity of channels not being interfered with automatically increases, to make the resulting signal strength substantially independent of the withdrawal of the channel interfered with. e

This invention is illustrated for a specific type of signal, namely, a tonally modulated signal such as in radio telephony or in tonally modulated telegraphy. Furthermore, the channels used are regularly spaced on a frequency basis. This arrangement is for illustration only, and the invention applies regardless of the frequency allocation of the channels, and the nature of the signals conveyed. The only restriction is that each channel shall convey the same signal,

The term channel is further not to be considered synonymous with wave band, since channels may be made up by depending upon energy I from widely separated wave bands. Thus, for example, with four radiated frequencies a, b, c, and d, a receiver may be devised if desired with six channels, involving tuning to the difference be- -tween each radiated frequency and every other radiated frequency.

For purposes of illustration, however, each rchannel is identified with a single wave band, vmaking up a part of a broader wave band, and in particular the signal herein used is produced by .frequency modulation at a high audible or low .superaudible rate, in combination with amplitude .modulations at a low audible rate.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed {to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the mitter constructed in accordance With the invention;

Fig. 2 shows the spectral distributions emitted radiations;

Fig. 3 illustrates diagrammatically a modified form of transmitter in which the carrier is fixed;

Figs. 4, 5 and 6 illustrate the operation of the transmitter;

Fig. 7 depicts diagrammatically the general features of a five channel receiver; and,

Fig. 8 shows a typical diagram of one of the five channels depicted in Fig. 7.

Like reference characters denotelike parts in the several figures of the drawings.

In the following description and in the claims parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to the drawings, Fig. 1 shows a transmitter which includes a carrier energy generator I I, a modulation frequency oscillator I2, a power amplifier I3, a modulator I4, a preamplifier I5 and an antenna system I6.

The carrier energy generator II includes a triode tube H which is provided with a plate tank circuit I8 and a feedback coupling coil [9 to produce high frequency oscillations in a well known manner, which are adjusted by a variable condenser 20.

The oscillator I2, which is of well known and standard construction, is provided with an output coil 2| which is coupled to a plate coil 22 and of the a grid coil 23, which are shunted by condensers 25 and 26 respectively. The plate coil 22 is connected through a choke 21 to the tank circuit I8 and the grid coil 23 is connected through a choke 28 to the grid of the tube I1.

The power amplifier I3 includes a pentode tube I 30 the first grid of which is connected through a condenser 3i to the output circuit of the tube H. An inductor 32, a condenser 33 and a resistor 34 serve to bias the grid of the tube 30 and to permit radio frequency voltageto be established thereon. The output circuit of the tube 30 includes a tank circuit 35 and the secondary of a transformer 36 the primary of which is included in the output circuit of the modulator I4. The input circuit of the modulator I4 is connected through a transformer 37 to the output circuit of the preamplifier I5, the input circuit of which is connected to a microphone 38. The tank circuit 35 is coupled to a coil 48 which is connected through a condenser 4| to the preamplifier and by the antenna .IB may,

two resistors 66 and space between thecoils 68-and 69.-

antenna Hi, the coil 40 and condenser 4| forming a tuning circuit.

Operation The characteristics of the high frequency oscillations produced by the generator I l are varied by the output of the modulation frequency oscillator I2, as energy from this oscillator is inserted by the coupling coil 22 into the plate circuit of the tube I1 and by the coupling coil 23 into the grid circuit of the tube With the ratio of the couplings properly chosen, the oscillations generated by the tube will be frequency modulated at the frequehcygenerrted by the modulator l2 in a mannersimilar-to that described in my U. S. Patent 1,599,586. The 'output of the frequency modulated tube comprises the equivalent of a plurality-f continuous waves separated in frequency by an amount equal to the frequency generated by the modulator l2. This output serves as the carrier-waves of the plurality of channels.

The output of the tube I! is impressed through the condenser 3| upon the first grid of the tube of thepoweramplifier l3 which is plate modu-.

lated by the microphone 38 acting through the modulator l4. The modulated output of the power amplifier I3 is transferred to the antenna l6 by means. of the tank circuit and antenna tuning circuit -4|. These elements may be so designed as to reenforce the higher order side bands at the expense of the lower order sidebands so that substantially equal energy is radiated. on each channel.

The spectral distribution of the energy radiated for example, be as depicted in Fig. 2. As previously stated the energy on the channels may be equalized by choice of the antenna system or by other devices such as an equalizer between the carrier energy generator H and the power amplifier l3. This figure depicts the effect of frequency modulating a carrier wave at arelatively high modulating frequency and then amplitude. modulating the resultant wave format a relatively low modulat- ;result is a plurality of conamplitude modulated by the ing frequency. The tinuous waves each same signal. 7

As an alternative a. plurality of continuous waves could be independently established by a;- plurality of crystal controlled oscillators and the waves radiated from a plurality of antennas could be amplitude modulated all in accordance with the same signal.

The modified form of transmitter depicted in Fig. 3 comprises a crystal controlled oscillator 45, a buffer circuit 46, a phase splitting circuit 41, an electronic mixing amplifier 48, a push-pull modulator 49, a high modulating frequency source 5|], la distorting circuit cuit 52, a power amplifier 53, a a preamplifier 55.

The oscillator includes a triode tube 51, a piezo-electric crystal 58 and an output tankcirmodulator 54 and cuit 59 which is connected through a condenser 68 to the first grid of a pentode'tube fil'which forms partof the buffer circuit 48. The plate circuit of the tube 6| includes a tank circuit-'62,

which is connected through a condenser 83 to the phase splitter 41.

The phase splitter 41 comprises a condenser65, 61 in series with two coils 68 and 39 mounted at right'angles to each other and an output coil 1|] adjustably mounted in the 5|, a limiting cir-.

the coil 10 is connected through two condensers II and 12 to the push pull modulator 49.

The mixing amplifier 48 is shown as including two pentode tubes 13 and 14 and a tuned output tank circuit 15. The first grid of the tube 13 is connected to the phase splitter 41 and the first grid of the tube 14 is connected through a transformer 16 to the cathodeoutput circuit of push pull modulator-49, the plates of which are connected through chokes 11 and I8 and transformer -19 to the modulating source 50.

The output circuit of the mixing amplifier 48 is connected through a condenser 8| to the grid of a triode tube' 82 'which forms part of the distort- -.ing'-circuit 5| and which may be biased near cut off similar toa detector tube. The output circuit of tube'82 includes a tuned tank circuit 83 .which is connected through a condenser 85 and resistors 86 and 81 to the limiting circuit 52 which comprises two diode tubes 88 and 89 in reverse connection.

The limiting circuit 52 is connected to the-first grid of a pentode tubeBO which forms part of. the power amplifier 53 and the output circuit of which includes an output tank-circuit9l. The -modulator amplifier 54 is connected through a transformer 92 to the power amplifier .53 andby a transformer 93 -to the preamplifier. 55. ,LA microphone 95 is connected in the input circuit of the preamplifier 55. The output tank circuit 9| is coupled to an antenna circuit 96 including ,an

antenna 91.

Carrier frequencydetermining energy is generated by oscillator 45 which is stabilized by the piezo-electric crystal 58 and is tuned by the tank circuit 59. Energy from this circuit is impressed upon the buffer circuit 46 and thence through condenser 63 to the phase splitting circuit. By means of the adjustable rotor 10 the phase across this rotormay be adjusted to any desired relation to the phase across any fixed part. of the system,,such for example as the coil 69.

Voltage from the coil 39 isimpressed upon the grid of tube 13- while-voltage from the rotorlll 13 and 14 respectively. These energies are ammodulated wave.

plified and combined in the tank circuit 15.

By adjustment of the rotor Ill the combined carrier determining wave and the bands may be related as the central wave and first order side frequencies of a phase or frequency modulated continuous wave; that is the phase of one. side band is different from what it would be if the three constituents represented an amplitude This process of producing quasi-phase modulated energy is described in detail in U. S. Patents 1,935,776 and 1,976,393,

- issued to John Hays Hammond, Jr. The nature One Side' Of IB of the tank circuit energy is depicted in Fig. 4.

The output of thetank circuit 15 is impressed through-condenser 8| upon the grid circuit of the distorting tube 82.- As a result of the distortion effects produced in the circuit 5| there-appear 1 currents among others in the plate circuit of the tube 82 with frequencies centered at double the frequency of the central input frequency. In addition to the central frequency there are two orders of side bands as depicted in Fig. 5, with th central wave and side bands arranged as in phase modulation. The output tank circuit I5 is tuned to the vicinity of this double frequency.

This more complex modulated wave form may be impressed upon further distorting and limiting devices, such as the diode tubes 88 and 89 which cut off the peaks of the impressed waves and tend to develop further order side bands, so that the distorted wave more nearly approaches a true phase modulated wave form. This process of limiting is shown for example in U. S. Patent No. 1,560,206, issued to Emery Leon Chaifee and as applied to minimizing amplitude modulation is shown by devices 28 and 29 of Fig. 2 in U. S. Patent No. 1,977,439, issued to John Hays Hammond, Jr.

The plurality of continuous wave equivalents produced by this method are impressed upon the tube 90 and after amplification are modulated at speech or other tonal frequencies from plate modulation transformer 92 which is driven by modulation amplifier 54 from preamplifier 55 actuated by microphone 95. This modulated energy is impressed by the plate to antenna coupling system, comprising the tank circuit SI and antenna circuit 96, upon the antenna 91. It is to be understood that the coupling and antenna systems may be so arranged as to reenforce the side band energy at the expense of the carrier to make the energies on the various channels substantially equal, as indicated in Fig. 6.

While means have been shown for producing five channels each modulated by the same audio frequency signal, it is to be understood that the number of channels could be increased to any desired amount by the use of successive distortions. Other systems could, as above stated, be readily devised to provide other than the simply related channels here indicated.-

The signals radiated from the transmitters shown in Figs. 1 or 3 may be received and interpreted by a receiver of the type depicted in Fig. 7 in which the five channels are designated by block diagrams, an illustrative example of one or which is shown in Fig. 8.

The receiver shown in Fig. 7 comprises an antenna I00, a beat detector IOI, an oscillator I02, five channels I03-I0'I and a set of head phones I08.

The antenna I is connected to the tuned circuit IIO which in turn is connected to the first grid of a pentagrid tube III, which forms part of the beat detector I M. The third grid of the tube III is connected to a tap on the grid coil I I2 of the oscillator I02. The grid coil H2 is inductively coupled to the plate coil H3 and a vernier condenser H5 is connected between the plate and ground.

Connected in the output circuit of the beat detector IOI is a primary tuned circuit H6 which is inductively coupled to a secondary tuned circuit III. The secondary circuit III is connected to bus conductors I I8 and I I9 which are connected to the input terminals I20 and .I2I of the five channels I03 to I01. The grid return end of the circuit H0 is connected through a resistor I22 to bus conductor I23 which is connected to the automatic volume control terminals I25 of the five channels I03 to I01.

. The output terminals I26 and I2! of the'five I45 forming part of the detector I32.

channels I03 to I0! are connected to bus conductors I28 and I29 respectively, which in turn are connected to the headphones I08.

In Fig. 8 is shown a possible arrangement of one of the five channels, the others being preferably similar except as to the circuit constants. Each channel comprises an amplifier I3I, a detector I32, a second amplifier I33 and a recti- .The input terminals I 20 and I2I are shunted by a potentiometer I36 the adjustable contact of which is connected through a condenser I31 to the first grid of a pentode tube I 38 which forms part of the amplifier I3I. The grid -of this tube is connected to ground through a resistor I 40 and a condenser I4I.

Connected in the plate circuit of the tube I38 is a primary tuned circuit I42 which is coupled to a secondary tuned circuit I43 which in turn is connected to the rectifier portion of the tube A resistor I46, shunted by a condenser I41, is included in the rectifier circuit. One end of the resistor I46 is connected through a condenser I48 to the grid of the amplifier portion of the tube I45 which is suitably biased by a battery I49. The output circuit of the tube I45 is connected thrugh a, transformer I50 to'the output terminals I26 and I21.

The adjustable contact of the potentiometer I36 is also connected to the first grid of a pentode tube I 5I forming part of the amplifier I33 the output circuit of which includes a tuned circuit I52. The plate of the tube I5I is connected through a condenser I53 to the plate of a diode tube I55 forming part of the rectifier circuit I34. A resistor I56 is connected between ground and the plate of the tube I 55 which is also connected by a resistor I5'I to the junction of resistor I40 and condenser MI. The cathode of the tube I5I is connected to ground through a potentiometer I58 the adjustable contact of which is connected through a resistor I59 to the cathode of the tube I55. I

In the receiver shown in Figs. 7 and 8 the incoming signals from all the channels of the trans mitter depicted in Fig. 1 or Fig. 3 are received by the antenna I00 and are transmitted through the tuned circuit III) to the beat detector IOI where they are impressed upon the first grid f the tube III. Heterodyning energy of suitable strength from the oscillator I02 is impressed upon the third grid of the tube III which is suitably biased. The oscillator vernier condenser I I5 is suitably adjusted so that the output of the tube III, representing the incoming signal suitably matches the characteristics of the subsequent circuits. the use of the oscillator I02 and associated circuits is well known and need not be more fully described herein.

The output energy of the beat detector I 0| is impressed upon the primary tuned circuit H6 and inductively into the secondary tuned circuit I IT. This energy is similar to the impressed antenna energy except as to the change of frequency. The output energy of the circuit H1 is impressed upon the bus conductors H8 and H9 and is distributed to the input terminals I20 and I2I of the five channels I03-I0I.

Referring to Fig. 8, relating to a selective sys- I tem corresponding for example to the next to the last channel of Fig. 6, the energy received at the terminals I20 and I2I is impressed upon thepotentiometer I36 from which part of the energy The method of frequency conversion by' passes through the condenser I31 and is impressed upon the first grid of' the amplifier tube I38 which is biased by voltage existing or developed across condenser I4I. The amplified energycorresponding to the desired channel is selectively transferred through the coupled circuits I 2-l43 to the rectifier portions of the detector tube M5 the rectified output from which passes through the resistor I46 in the direction of the arrow. This rectified energy serves to produce tonal energy for signal purposes and D. C. energy for volume control purposes. The tonal energy is transferred through the condenser MB and is impressed upon the grid of the.

amplifier portion of the tube Hi5, which is suitably biased by the battery I49. The output energy of; the tube M5 passes through the transformer I58 to the output terminals I26 and i2! and thence along bus conductors I28 and I29 to the headphones Mil. (Fig. 7).

The direct voltage developed across the resistor I46 is fed back through resistor IN to the terminal I25, thence combined with direct voltage similarly developed in other channels is fed along bus conductor I23 and resistor I22 to the grid circuit of the tube It Ito operate as an automatic volume control of the prior circuits in a well known manner.

For controlling the operation of the amplifier I,3I some of the energy from the potentiometer I36 is impressed upon the grid of the amplifier tube l5l. The amplified energy from the amplifier I33 corresponding to that transferred through circuits M d-Hi3 is selectively transferred through the tuned circuit E52 and is impressed through the condenser I53 upon the plate of the diode rectifier tube I55. The cathode of the tube M55 is positively biased by the potentiometer I58 which carries the cathode-ground current of the tube I5I.

The adjustment of the potentiometer I58 may be made so that for a normal signal no rectification will be produced by the tube I55. If, however, an abnormal amount of energy passes through the circuit I52,'indicative of interference upon this particular channel, then the rectifier I34 operates to develop a negative voltage on the plate of the tube G55 with respect to ground due to the flow of rectified current through the resistor I56 in the direction of the arrow. This negative potential is impressed through the resistors I51 and I413 upon the grid of the tube I38 increasing the bias in accordance with the intensity of the interference, thereby reducing the amount of signal and also the interference which is delivered from the tube I55 to the headphones H38.

Because the control of the grid of the tube I38 is from a separated channel and notthe output of the tube I38, as is usual in automatic volume control arrangements, the tube I38 may be biased so that'with strong interference, no signal whatever will pass through this channel. In the absence of signal through the channel the voltage developed across the resistor I 36 falls off so that it contributes little or nothing to the automatic control voltage impressed backupon the preceding tubes, such as tube I I l of Fig. '7. Therefore the bias on the preceding tube diminishes and the signal available for the other channels increases. In this manner'thesignal to the head phones H18 will remain substantially constant as long as there is one clear channel on which abnormal interference does not exist.

Under-normal operation the various potentiometers was of the five. channels I'03'-l 01' are so ad'- justed that each of'the five channels contributes substantially the same amount as every other channel to the output signal.v

It is to be understood that the receiver shown is for purposes of illustration only. Further amplifiers and selective devices maybe used to improve the performance and operation. For example while the present arrangement utilized linear first detector NH and amplifiers I3I and I33 at levels not readily subject to overload, under abnormal conditions the tubes I38 and [SI which are exposed to interferences which exist on other channels might be paralyzed. In this case a design in which the input to each channel, such as shown in Fig. 8, is protected by tuned circuits would be preferable by which the system could be paralyzed only by interferences which have the same frequency ranges as the channel normally transmits These and other modifications are omitted for simplicity and would occur to anyone skilled in the art in the development of a system of this broad type.

Although only a few of the various forms in which this invention may be embodied have been shown herein, it is to be understood that the invention is not limited to any specific construction. but might be embodied in various forms without. departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. The method of signaling which includes the steps. of producing a carrier wave, producing a modulation frequency wave, frequency modulating the carrier wave by the modulation wave to produce a plurality of continuous waves separated in frequency by an amount equal to the frequency of the modulation wave, producing signal energy, amplitude modulating the resultant plurality of continuous waves by the signal energy, reenforcing the higher order of side bands at the expense of the lower order side bands so that substantially equal energy. is available on each channel and transmitting the resultant energy.

2. In a signaling system wherein a plurality of continuous waves each of a different frequency are modulated by the same signal energy and transmitted, means for receiving the transmitted energy including a main channel for transmitting all of said waves, a plurality of translating channels one for each of the received waves, said main channel being coupled to said plurality of channels, means for appreciably decreasing the sensitivity of any one of said plurality of channels when the magnitude of the energy fed thereto exceeds a predetermined value, and means in saidone channel for automatically increasing the sensitivity of the main channel, as the sensitivity of the one channel is reduced, to such an extent that the total signal output from said plurality of channels remains substantially the same.

3. The steps in a method of signaling which comprise, producing carrier frequency nergy, splitting the phase of the produced energy, producing a modulating frequency wave, modulating one of'the split phases by the modulating frequency Wave to produce therefrom first order sideband output ener y, combining carrier frequency energy with the resultant first order sideband output energy, the phase which is modulated being adjusted so that the combined carrier determining wave and the first order sideband output energy maybe related as the central wave andfirst order side frequencies of a timing modulated continuous wave, distorting the combined energy to such an extent that there result currents with frequencies centered at double the frequency of the central wave and two orders of sidebands with the central Wave and sidebands arranged as in phase modulation, modulating the resultant energy in accordance with signal energy and transmitting the energy thus modulated.

4. The additional step in the method described in claim 3 which comprises reenforcing the higher order of sidebands of the signal modulated energy at the expense of the lower order of sidebands.

5. In a diversity broadcasting system including transmitting means for transmitting a plurality of carrier waves of different carrier frequencies all modulated by the same signal, a diversity receiver for receiving the transmitted waves, said receiver including an electronic tube amplifier having an input circuit upon which the received waves are impressed and an output circuit, a plurality of signal translating channels, one for each of said waves coupled to said output circuit, each of said channels including means for applying to said electronic tube amplifier a biasing potential the magnitude of which depends upon the strength of signals passing through the channel, means in each of said channels for substantially suppressing translation by said channel when the amplitude of the energy transferred to said channel from said amplifier exceeds a predetermined value, and means controlled thereby for correspondingly varying the biasing potential applied to said tube by said channel in a direction to increase the amplification of said amplifier.

6. In a diversity broadcasting system including transmitting means for broadcasting a plurality of modulated continuous waves of difierent carrier frequencies but all modulated by the same signal, a diversity receiver for receiving the transmitted waves, said receiver including an electronic tube amplifier having an input circuit upon which the received waves are impressed and an output circuit, a plurality of signal translating channels one for each of said waves coupled to said amplifier output circuit, each of said channels includtrolling the amplification of said amplifier so as to produce a predetermined desired total output from said channels, means in each of said channels for varying the translation by the channel inversely with the amplitude of the energy transferred to said channel from said amplifier circuit,

each of said means acting to substantially suppress translation in its corresponding channel when the magnitude of energy transferred to said channel from said amplifier circuit exceeds a predetermined value.

'7. In a signaling system, means for generating a carrier frequency wave, means for frequency modulating the generated carrier at a relatively high modulating frequency to thereby produce a plurality of continuous waves separated in frequency by an amount equal to the frequency of the modulation wave, means for amplitude modulating the resultant waves at a relatively low modulating signal frequency to thereby produce a plurality of continuous waves each modulated by the same signal, means for transmitting the waves so modulated, means for receiving the transmitted waves and separating out each channel, means for detecting each of the Waves in the channels to produce therefrom the signaling energy, means for combining and reproducing the signaling nergy.

8. The arrangement described in claim 7 characterized by that each of the channel detecting means includes means for reducing transmission therethrough when the input signal thereto becomes excessive and automatically increasing the sensitivity of the other channels to such an extent as to make the final signal independent of the number of channels operated.

ELLISON S. PURINGTON. 

